Air springs have been used for some time to level or to raise vehicles for whatever desired purpose, such as when the cargo changes or for off-road travel. These air springs are disposed between the wheel's axle or axle support (the unsprung mass) and the chassis (the sprung mass). When deflated, the chassis is lowered to rest upon the axle or support, the chassis being supported by, for example, rubber stops or the like. When inflated, the chassis is raised relative to the axle or support to the desired height. Shock absorbers are also typically provided between the chassis and the wheel axles or supports to dampen relative motion between the chassis and axles.
To raise the chassis, the air spring or springs are inflated, usually manually or, recently, by suitable controls. The pressure of the compressed air within the spring rises resulting in a corresponding lifting of the chassis by the air springs.
If the cargo or passengers are not evenly loaded on the chassis, the pressure of one or several of the air springs must be adjusted to maintain the chassis level. Accordingly, sensors such as position transducers or proximity switches must be provided at some or all of the air springs if automatic control is to be achieved. The location of the sensors and the appropriate connecting wires from the sensors to the control have caused concern from a cost and reliability standpoint in that the switches are subject to corrosion, road grime or the like. For manual control, each air spring must be adjusted whenever the loading of the chassis changes. Adjustment of the springs as loading of the chassis is altered is time consuming, requires an outside source of compressed air and is laborious.